Many applications require light sources that emit uniformly white light. Some light sources provide white light through the mixing of light of different colors. In practice, light emitted by these types of light sources is often not uniformly white in the far field where the light source appears as a point source, and various techniques for color correction are known in the art. WO 2013/035036 A1, for example, discloses collimators having rotationally symmetric surface segments designed to correct so-called “color over angle” (CoA) variation. In short, CoA variation results from the color of the emitted light being dependent on the angle of emission.
Another example of an undesirable color variation that may occur is known as “color over position” (CoP) which refers to situations where the color of the emitted light depends on the position of emission on the light source. It is possible to use collimators for reducing CoP variation, but different technical requirements have to be met compared with the case of CoA variation.